The present invention relates to a method and apparatus for examining a substance to characterize its type and composition. The invention is particularly useful for examining tissue in order to characterize it as cancerous or non-cancerous, and the invention is therefore described below with respect to this application.
Today, in many surgical applications there is a need to cut biological tissues of a specific type while avoiding cutting tissues of other types. For example, in a tumor removal surgery, the surgeon attempts to cut around the tumor in order to remove it. There are many ways to perform this medical procedure but all share the same fundamental principle: Never cut through a tumor. This principle is the core of good practice and markedly affects the success rate of tumor removal procedures. Failing to keep this fundamental rule increases the failure rate of the surgery, the reoccurrence rate of the cancer, and the rate of necessary re-excisions.
Nevertheless, during surgery the surgeon does not have (except for his trained eyes and fingers) any real-time indication of the kind of tissue that is being cut. Furthermore, if the surgeon cuts through healthy tissue and then, accidentally, cuts a small portion of a malignant tissue, this will be noticed, if at all, only in the pathologist report after conducting a biopsy. Therefore, from the point of view of organ conservation and reoccurrence rate reduction, it is highly desirable to use a real time tool that displays the type of tissue being cut and alerts the surgeon whenever a tumor is about to be cut.
In many medical procedures, the diagnostics tool and surgical assist tools are serially applied to the patient in order to increase the specificity and sensitivity of the tests. When trying to perform such serial examinations during surgical operations, the problem of coordinate registration becomes a crucial one. Therefore, a tool that enables simultaneous measurement of multiple, independent tissue characterization modalities in the same place (i.e. of the same biological mass) possess an added and synergetic value.
There are numerous modalities, methods and devices that have been developed in order to differentiate and characterize tissue as being malignant or healthy. Still, use of multi-modality tissue sensing and characterization probes, as described, for example, in U.S. Pat. No. 6,109,270 and US 20030045798, has the possibility of enhancing the differentiation capabilities of the device.
The ability of detect cancer cells, and especially breast cancer, using electric impedance of tissue is well established in the biomedical literature1,2,3,4. Another technique, based on magnetic bioimpedance5, measures the bioimpedance by magnetic induction. Although the exact mechanism responsible for tissue impedance at various frequencies is not completely understood, the general mechanism6,7 is well explained by semi-empirical models that are supported by experiments8,9,10.
Variations in electrical impedance of the human tissue are used in, for example U.S. Pat. No. 4,291,708 and U.S. Pat. No. 4,458,694, to provide indications of tumors, lesions and other abnormalities. Millimeter and microwave devices are used, for example in U.S. Pat. No. 5,807,257, U.S. Pat. No. 5,704,355 and U.S. Pat. No. 6,061,589, to measure bioimpedance and to detect abnormal tissue. Additionally, commonly owned U.S. Pat. No. 6,813,515 discloses a method and apparatus for locally characterizing tissue by its Electric Impedance properties.
MRI has long been recognized as a useful modality/method for tissue characterization as malignant or healthy. MRI is “global” method, which requires positioning of the patient within the apparatus, and is therefore not suitable for use during an operation procedure. Variations of the MRI modality which provide a local MRI probe have been disclosed, for example, in U.S. Pat. No. 5,572,132 where a MRI response is detected in an intravascular device, in WO0239132 where a variation of the intravascular approach is presented, and in U.S. Pat. No. 6,489,767, where a local MRI surface characterization method is disclosed
Motion is another problem in any real time imaging or detection tool, such as Magnetic Resonance Imaging (MRI), that demands stationary objects for good imaging results. For example, during breast surgery, the movement of the breast with breathing is a major problem for achieving good resolution. An in situ miniature real-time tool that moves with the body avoids the motion problem. When such a detection tool also possesses an in-situ marking capability, the problem of coordinate registration is substantially eliminated.